1. Field of the Invention
The present invention relates generally to braided structures and to methods and apparatus for producing braided products or braided reinforcement.
More specifically, the invention is directed to an improved braided reinforcement for tubular conduits such as hose characterized by a three over, three under braid pattern. The invention further is directed to a method and apparatus for producing a three over, three under braid structure utilizing a Maypole type braider.
2. Description of the Prior Art
Braided structures have long been used to provide a combination of strength and flexibility to products such as rope and cable formed of yarn or wires as well as to flexible tubular structures in the form of reinforcement, for example hose for high pressure service covered with a braided yarn or wire reinforcement.
The conventional form of braided reinforcement for flexible conduits such as hose employs a "two over, two under" braid configuration. This has been the standard braid pattern for tubular braid structures and virtually all apparatus for forming such structures has been built to produce a two over, two under braid. Efforts to increase the performance of conventional two over, two under reinforcement have focused on the use of stronger materials, increased utilization of the available strand space, the twisting of the strands, and pressurized treatment of the braid structure prior to use. However, all of these efforts have been made in the context of a conventional two over, two under braid pattern.
The conventional braided reinforced hose comprises a plurality of flat strands of parallel yarns or wires, the wire being typically employed for high pressure hose. Since the burst strength of reinforced hose is essentially dependent upon the amount of material in the braided reinforcement, improved hose strength could be achieved by utilization of a plurality of braided layers. Such an approach is expensive in that a second braiding operation is required, and a second braided reinforcement does not effectively serve to double the hose burst strength.
A significant departure from the conventional flat braid comprised of carefully controlled parallel wires is disclosed in the Slade U.S. Pat. No. 3,463,197, wherein a mounded strand configuration utilizing a large number of small wires was proposed. This approach provided markedly improved hose performance, particularly in terms of impulse strength and has been widely used in high pressure hose applications, particularly in the aircraft industry. U.S. Pat. No. 4,567,917 to Millard adds a further step to the mounded configuration proposed by Slade, namely the preforming of the wire and the twisting of the strands to more equally distribute the pressure loads on the strand wires.
Despite the proposed changes in configuration of the strands and the materials and number of ends comprising each strand, a constant characteristic of braided reinforced hose over the past fifty years has been the utilization of the standard two over, two under braid pattern. The reinforcing braid proposed by the present invention departs markedly from this accepted standard.
The methods employed and the apparatus utilized in producing a conventional two over, two under braid vary to some degree, but fall basically in two categories. The first is the so-called Maypole or sinuous braiding technique wherein the strand carriers are moved in an intersecting serpentine path on a braiding deck as the strands are let off under tension onto the tubular element to be reinforced which is pulled at a uniform rate in a direction perpendicular to the deck. Although early forms of Maypole braiders utilized mechanisms for driving the carriers in opposite directions around sinuous tracks mounted on the braider deck, modern Maypole braiders utilize planetary gearing and a cam track and cam follower system on the carriers and drivers to eliminate the tracks and their attendant high friction and wear problems. An example of such a modern planetary gear type Maypole braider is shown for example in my U.S. Pat. No. 3,783,736, issued Jan. 8, 1974.
In a second type of braiding technique, the strand carriers are arranged in two annular groups which are axially spaced with respect to the tube to be reinforced. The groups are rotated in opposite directions with respect to the tube and a mechanism is provided for alternately guiding the strands from the outer group of carriers over and under the carriers of the inner group. Apparatus for carrying out this second technique is known as a rotary braider, an example of which is disclosed in U.S. Pat. No. 4,034,642 issued July 12, 1977.